“Polarized training” is a fancy new name for a basic old concept—train either at low or high intensity, but keep the moderate training time between these extremes relatively small. So what are low, moderate and high intensities? All of the recent polarized research studies define them, usually using heart rate as the standard, as follows…
Low. Called “zone 1.” Below the ventilatory threshold which is, essentially, the aerobic threshold (AeT). AeT is best determined in a lab test. It’s very roughly 30bpm below your anaerobic threshold (or lactate threshold, functional threshold, etc). This is a very easy workout that is commonly used for active recovery. (The reference to zones here is strictly for the purposes of these studies and not the same as the zones normally used by athletes.)
High. Called “zone 3.” Most of the studies use the respiratory compensation threshold. For our purposes, that is the equivalent of your anaerobic threshold (AnT). AnT is the intensity above which breathing becomes labored. This is a very hard workout intended to improve performance.
Moderate. Called “zone 2.” As you might have guessed by now, this is the range between AeT and AnT.
The most recent study on this subject was reported in the May 2013 edition of the International Journal of Sports Physiology and Performance (1). A group of researchers from the European University of Madrid assigned 10k runners to either a polarized (emphasis on low intensity—zone 1) or a between-thresholds (emphasis on moderate intensity—zone 2) training protocol for 10 weeks. After the training period they repeated a 10km race on the same course used to establish a baseline before the 10-week period began. Both groups improved their performance times, but the polarized (low-high/zones 1 and 3) improved by 41 seconds more than the between thresholds (moderate-high/zones 2 and 3) group. The high intensity training time was about the same for both groups. The only thing that differed was how much time was spent in the low (z1) and moderate (z2) ranges.
The accompanying table summarizes this Spanish study along with two other older studies that followed a similar protocol (click to enlarge). Note that the groups which trained low-high performed better in the post-tests than the groups that trained moderate-high—in all three studies. (You can read the abstracts for each of the studies by clicking on the references below.)
Two other studies in the last few years took a look at how athletes distributed their intensities as they trained for real-world competitions. The first of these, from the same Spanish researchers again, followed 8, sub-elite, young (23 +/- 2 years old), male runners as they prepared over a 6-month period for the national cross country championships (4km and 10km) (4). Their average intensity distributions were:
Z1 = 71.3%
Z2 = 21.0%
Z3 = 7.6%
The researchers found that there was a close correlation between how much time was spent in zone 1 and performance time. In other words, the more zone 1 training, the faster they raced.
A second study out of Norway followed 11 junior Nordic skiers for 32 days of normal training and observed their intensities based on heart rate, ratings of perceived exertion (RPE) and lactate samples (5). The distributions for each of these testing methods was remarkably similar so I’ll just report heart rate distribution as the other studies have done:
Z1 = 75%
Z2 = 8%
Z3 = 17%
Following athletes as they train in the real world is often more revealing than lab studies. Note that the runners in the latter Spanish study did relatively little zone 3 training having 92% below AnT (combined zones 1 and 2). This is what I would expect to see from self-coached athletes. The Norwegian skiers had coaches, as we can tell from the lactate samples being taken. Note that they appear to have polarized the training intensities quite nicely.
One take-home message here is that there is nothing wrong with training below your aerobic threshold. In other words, really easy. Recovery is important. Too many athletes think the way to better performance is to raise the intensities on their recovery days. Not good. Easy, recovery workouts must be done in zone 1. And due to a lot of one’s training time being spent in zone 1, the quality of the high-intensity workouts (zone 3) improves. Doing a lot of zone 2 for recovery may well detract from your capacity to do the more valuable training above the anaerobic threshold.
Actually, I wish it was that simple. In the real world there are races done right smack-dab in zone 2, between AeT and AnT. For example, the race intensities of marathons, half marathons, Ironman and 70.3 triathlons all fit into this category. In fact, almost any race longer than an hour is a zone 2 event. One exception is road cycling in which the outcomes are determined largely by zone 3 (>AnT) efforts even though the race is mostly zone 2. So should you avoid training in this “toxic” zone? Perhaps not. It depends on what you are training for. As I continue to hammer home: You must prepare for a race by making your training increasingly like the race as you get closer in time to it.
The bottom line here is that the real issue is hard-easy training, not necessarily training predominantly in zones 1 and 3. It just so happens that each of the cited studies used subjects training for relatively short events. But that may not be you. Chances are it isn’t. So let’s say you are training for a 70.3 triathlon. Doing a workout with several 20-minute intervals in zone 2 (between AeT and AnT) with short recoveries could easily be a hard workout and yet not exceed AnT.
So “hard” is best defined relative to what you are training for and what the total stress load of a given workout may be—not necessarily what heart rate zone you were in. “Easy” is more easily defined, regardless of event duration, as being below your AeT.
Are you training in this way? The challenging part for most athletes is getting a lot of zone 1 time. But that’s the starting point. The quality and volume of your “hard” workouts will never be hard enough if you insist on trying to recover above your AeT.
2. Neal CM, Hunter AM, Brennan L, et al. 2013. Six weeks of a polarized training-intensity distribution leads to greater physiological and performance adaptations than a threshold model in trained cyclists. J Appl Physiol 114(4):461-71.